By modern semiconductor manufacturing techniques, a larger number of devices, either integrated circuits or discrete devices or thin film head, are manufactured on a single slice or wafer of semiconductor material usually 2 to 8 inches in diameter and about 18 thousandths of an inch thick. Thin film heads for Winchester disks are also made with the process using ceramic or silicon carbide substrates that range in thickness from 1 to several millimeters. The wafers and substrates are later cut into individual devices which are packaged in individual enclosures to make the finished device.
During the processing of each wafer, several patterned etching steps must be performed. The patterns are typically applied by coating the wafer with a photosensitive film which is exposed to light through an opaque mask in the shape of the desired pattern. Upon development, the remaining film forms an adherent etch resistant coating on the wafer in the pattern of the mask.
However, this automated, computer controlled alignment process does not overcome the problems which semiconductor manufactures are experiencing, particularly those in the thin film head business, with regard to the patterning of substrates with variable thicknesses. The thickness variation of the substrate or wafer often exceeds the total range of focus accommodation built into the stepper and requires that an awkward and time consuming mechanical change be made in the wafer chuck each time a new variety of device is patterned.
Conventional semi-automatic wafer thickness compensation mechanisms require that the thickness increment be manually selected. A chuck pedestal typically incorporates a manual adjustment for the wafer or substrate thickness. The thickness increments are mechanical in a precise step function. Each step has its own built-in sensor for the system's requirements.
After the operator has manually selected the desired thickness increment on the chuck pedestal the wafer is loaded onto the system by moving the stage to a wafer load slot. The wafer chuck picks up the wafer and leaves it in the up position during the coarse alignment routine. Thereafter, the stage travels out of the load slot and the moveable pedestal will retract to its down position. The system will then re-check the thickness clearance settings and, if positive, proceed underneath the air probes for the initial focus set point and begin to step and print. After completing the step pattern the stage will move toward the out slot. The moveable pedestal fully extends and the stage proceeds to an out slot and deposits the substrate on its track. Thereafter, the stage returns to the wafer load slot and a new load cycle can begin.
The present inventor has developed a fully automatic thickness compensation actuator system which overcomes the need for mechanical detection and mechanical adjustment of the pedestal when wafers of variable thicknesses are used. It allows for--automatic thickness compensation for a variety of wafer or substrate sizes by means of a computer or microprocessor controlled actuator disposed below the vacuum chuck. The thickness compensation is achieved by enabling the height of the wafer to be automatically and continuously calibrated or adjusted with respect to the variable thickness such that the upper surface of the wafer will always be in a predetermined plane.
The present invention also provides many additional advantages which shall become apparent as described below.